Why does my FORTRAN code produce a different answer outside of MATLAB than inside of my MEX-file?

When I run my FORTRAN code as a standalone executable, I receive a different answer than when the same code is called from inside my MEX-file.

Answer 1

[MathWorks Support Team]

This is due to how MATLAB sets up the floating-point operations in the CPU at startup, and is not a bug in MATLAB.

If you use the following C code in your FORTRAN program, you should see the same answers:

 void ResetFPU() 

 { 

     const static int CtrlWord=0x123f; 

 __asm  fninit //initialize fpu 

 __asm  fnclex   // clear fpu exceptions 

 __asm  fldcw  CtrlWord     // Load_FPU_Control_Word; 

 }